In the known apparatus of this sort regularly a different die has to be mounted in order to accommodate the groove extending in the die as to its shape and size in accordance with the kind and the thickness of sheet material to be bent and the desired shape to be bent. Exchanging the die, however, is relatively time consuming.
An other serious draw back of the known apparatus is that during bending of the sheet material the surface thereof slides along the groove defining edges of the die whereby a strong wear of the die is effected, while the accuracy of the dimensions of the shape to be bent is reduced. Furthermore, the sliding of the surface of the sheet material to be bent along the said edges of the die requires large forces for the deformation of the sheet material, while furthermore the surface of the sheet material may be easily damaged.